This report describes the production of a tetramethylurea reference material (IRMM-425), certified for its deuterium-to-hydrogen (D/H) ratio. The material is to be used as an internal standard in site-specific natural isotope fractionation - nuclear magnetic resonance (SNIFNMR) spectroscopy measurements for determining the D/H ratios of ethanol distilled from wines, an important measure in wine authenticity testing (Commission Regulation 2676/90, (1)). Commercially obtained TMU with a sufficiently high D/H ratio (> 120 ppm) was purified by removing most of the residual water and filled into amber glass ampoules in 7.8 mL portions. Homogeneity was tested and no heterogeneity observed. Stability studies indicated no material degradation for 4 weeks at 60 °C and for 18 months at -20 °C. Batch charactersation was accomplished in an inter-laboratory comparison using the SNIF-NMR technique exclusively.
The certified value was obtained as the unweighted mean of the laboratory means of the accepted sets of results. The expanded uncertainty associated (k = 2) includes contributions from (potential) heterogeneity, potential instability, characterisation, as well as the carried-over uncertainty from BCR-656. Due to its negligible contribution, the uncertainty associated with the purity of the material did not need to be included. The certified value and its associated uncertainty are 141.9 ± 0.7 x 10 to the power of -6. This CRM constitutes a master batch and will be used for the certification of secondary batches; the material is not for sale.